Conventional apparatuses are, for example, those which are disclosed in Patent Document 1 and Patent Document 2. According to these apparatuses, a polylactic acid is produced by concentrating lactic acid to reduce the content of water and then polycondensing the concentrated lactic acid to produce a lactic acid oligomer, once depolymerizing the lactic acid oligomer with addition of a catalyst such as antimony oxide, thereby to obtain an annular dimer (lactide), if necessary, carrying out purification by crystallization or the like, and thereafter opening ring polymerizing the lactide with addition of a catalyst such as tin octylate to produce a polylactic acid.
Patent Document 1 discloses an apparatus including a lactide-forming reactor which depolymerises lactic acid oligomer and a condenser which condenses evaporated lactide, with a reflux condenser being provided between the lactide-forming reactor and the condenser.
Patent Document 1: JP-A-11-217425
Patent Document 2: JP-A-10-168077